When you get a boner and there's no way or time to hide it from others sight. It's so big and flaring that it can't and won't go away and everyone sees it. Just like the devil is controling your weeny.Most likley ending in a huge orgy with everyone within a 666 mile radius.

clark: dude in p.e. last week i was eyeing sarahs booty it was tight, and gave a gnarly satan boner.Then, the teacher told me to stand up and demonstrate a pull-up.Dude everyone saw and laughed until the devil took over and we all had an orgy on the softball field.
tim: sounds cool she's hot.

The most common case is when you wake up and have a massive boner that cannot be silenced. Other and more crucial times the boniferus luciferus can occur is when you're in P.E. class sitting during roll call and you be eyeing some girl. Suddenly the teacher will ask you to get up to play and you got a fat wood to show to the whole class. Signs of the satan boner are a 666 on your nuts.

I was checking out jessica when I gothit with the satan boner that poked her in the head it was so devlish.